The BBC may have bowed to political pressure to show bias against Labour and Jeremy Corbyn, a former chair of the BBC Trust has said.

Sir Michael Lyons, who chaired the trust from 2007 to 2011 and is a former Labour councillor, claimed that there had been “some quite extraordinary attacks on the elected leader of the Labour party”.

He told the BBC’s The World at One: “I can understand why people are worried about whether some of the most senior editorial voices in the BBC have lost their impartiality on this.

“All I’m voicing is the anxiety that has been expressed publicly by others … We had here a charter review process which has been littered with wild kites flown which, we can’t see the string is held by the secretary of state, but the suspicion is that actually it’s people very close to him.

“His own comments have suggested that he might be blessed by a future without the BBC. Is the BBC strong enough to withstand a challenge to its integrity and impartiality?”

Lyons said there were “very real suspicions that ministers want to get much closer to the BBC, and that is not in anybody’s interests”.

Labour has complained about media bias against the party without singling out the BBC. Corbyn told grassroots supporters that it was necessary for Labour to use social media to communicate with the public, because rightwing media were censoring political debate in an unprecedented assault on the party.

Tony Hall, the BBC director general, also speaking to the The World at One, said Lyons’s claim was “extraordinary” and denied that there was any bias.

“That’s not the journalism I know or the journalists in this organisation I know,” he said. “I think the journalism of the BBC is impartial. We test all sides. The journalists in the BBC do a really hard job in the midst of controversy, bringing a light and calm judgments to what’s going on.”